Method of detecting an integrated circuit in failure among integrated circuits, apparatus of doing the same, and recording medium storing program for doing the same

ABSTRACT

There is provided a method of detecting an integrated circuit in failure among integrated circuits, based on spectrum which is a result of analyzing a frequency of a current running through an integrated circuit when a test signal is applied to the integrated circuit, comprising the steps of (a) assuming that all integrated circuits under test define a under-test integrated circuit set, and testing each one of the integrated circuits in the under-test integrated circuit set in a conventional manner, (b) removing integrated circuits having been judged to be in failure in the step (a), from the under-test integrated circuit set, (c) measuring spectrum of a current supplied from a power source into each one of the integrated circuits in the under-test integrated circuit set, (d) calculating both a mean value and standard deviation of the spectrum for the under-test integrated circuit set, (e) judging whether an integrated circuit is in failure or in no failure, based on both the mean value and the standard deviation of the spectrum, (f) removing integrated circuits having been judged to be in failure in the step (e), from the under-test integrated circuit set, and (g) judging the under-test integrated circuit set to be in no failure. The method makes it possible to find integrated circuits in failure without preparing data of an integrated circuit in no failure, as a reference.

This is a divisional of application Ser. No. 09/605,978 filed Jun. 29,2000, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of detecting an integrated circuit infailure among a plurality of integrated circuits, and more particularlyto a method of doing so, based on spectrum which is a result ofanalyzing a frequency of a current running through an integrated circuitwhen a test signal is applied to the integrated circuit.

The invention relates also to an apparatus for detecting an integratedcircuit in failure among a plurality of integrated circuits, and moreparticularly to an apparatus for doing so, based on spectrum which is aresult of analyzing a frequency of a current running through anintegrated circuit when a test signal is applied to the integratedcircuit.

The invention relates further to a recording medium readable by acomputer, storing a program therein for causing a computer to eithercarry out the above-mentioned method or act as the above-mentionedapparatus.

2. Description of the Related Art

A method of detecting an integrated circuit in failure among integratedcircuits has usually been carried out in order to detect and removeintegrated circuits which are not capable of performing desiredoperations due to defectiveness in fabrication steps, and ship onlyintegrated circuits which can properly operate.

For instance, the inventor had suggested a method of detecting anintegrated circuit in failure in Proceedings of the 1998 IEICE GeneralConference C-12-8 “Diagnosis of failure in an integrated circuit byanalysis of a current with power spectrum”. In this method, a currentrunning through an integrated circuit while the integrated circuit is inoperation is analyzed with respect to a frequency, to thereby detect anabnormal current caused by defectiveness in fabrication step.

Japanese Unexamined Patent Publication No. 9-33604 has suggested amethod of identifying a failure mode, comprising the steps of detectinga logic operation test pattern in which a power source currentabnormally runs through CMOS logic circuit, which is one of internalcircuits of an integrated circuit, in an amount greater than apredetermined amount while the CMOS logic circuit stops its logicoperation, when a logic operation test pattern is input into the CMOSlogic circuit through an input terminal thereof, extracting acharacteristic between a power source voltage and a power source currentwith the detected logic operation test pattern being input into the CMOSlogic circuit, and comparing the thus extracted characteristic between apower source voltage and a power source current to similarity between afailure mode and data between a power source voltage and a power sourcecurrent, stored in a database, to thereby identify a failure modeoccurring in the CMOS logic circuit.

Japanese Unexamined Patent Publication No. 9-211088 has suggested amethod of detecting a failure in CMOS integrated circuit by observing astatic power source current independent of switching of a transistor,among a current running through CMOS integrated circuit when a testpattern is applied to CMOS integrated circuit. The suggested method iscarried out in an apparatus including means for repeatedly applying atest pattern to CMOS integrated circuit under test, means for measuringa power source current supplied to CMOS integrated circuit under test,and means for measuring power spectrum of the detected power sourcecurrent. The method includes the step of judging whether CMOS integratedcircuit is in failure or not by observing a magnitude of power having apredetermined frequency band, among the power spectrum of the powersource current.

Japanese Unexamined Patent Publication No. 10-301843 has suggested adata processor comprising a main memory including a plurality ofmemories, and a plurality of processors transmitting a plurality ofrequests of data transfer to the main memory for each unit of data, andprocessing data transmitted from the main memory. The plurality ofmemories include means for detecting bank competition which occurs bythe requests transmitted from the processors, and transmit a bankcompetition signal to the processors, and a circuit measuring a periodof time during which bank competition occurs, based on the bankcompetition signal.

Japanese Unexamined Patent Publication No. 11-2663 has suggested amethod of detecting a failure in CMOS integrated circuit by observing astatic power source current running CMOS integrated circuit when aseries of test patterns is repeatedly applied to CMOS integrated circuitfrom LSI tester. The method includes the steps of repeatedly applyingtest patterns to an integrated circuit under test and a referenceintegrated circuit which is identical with the integrated circuit undertest and is not in failure, measuring a difference between a currentrunning through the integrated circuit under test and a current runningthrough the reference integrated circuit, and judging whether theintegrated circuit under test is in failure or not, based on a magnitudeof spectrum component having a repetition frequency at which the testpatterns are repeated.

Japanese Unexamined Patent Publication No. 11-94917 has suggested amethod of testing a semiconductor device on which CMOS circuit ismounted, comprising the steps of inputting a clock signal into thesemiconductor device, and calculating a maximum operating frequency onthe basis of an inverse number of a delay time during which a powersource current starts increasing at a clock operation timing and thenbecomes steadily equal to zero.

However, the above-mentioned methods are all accompanied with a problemthat a reference, that is, data about a power source current of anintegrated circuit having no failure has to be prepared in advance inorder to test integrated circuits under test.

It is quite difficult to prepare such a reference. The reason is asfollows. Data about a power source current is analog data, and is muchinfluenced by processing conditions in fabrication of an integratedcircuit. As a result, there is slight fluctuation among data about apower source current of integrated circuits having no failures. Hence,it is quite difficult to define a reference to be used for testingintegrated circuits as to whether they are in failure or not.

SUMMARY OF THE INVENTION

In view of the above-mentioned problem, it is an object of the presentinvention to provide a method of detecting an integrated circuit infailure among integrated circuits, without preparing a reference, thatis, data about a power source current of an integrated circuit having nofailures, by utilizing data about a power source current of integratedcircuits under test.

It is also an object of the present invention to provide an apparatusfor doing the same.

Another object of the present invention is to provide a recording mediumreadable by a computer, storing a program therein for causing a computerto carry out the above-mentioned method or act as the above-mentionedapparatus.

In one aspect of the present invention, there is provided a method ofdetecting an integrated circuit in failure among integrated circuits,based on spectrum which is a result of analyzing a frequency of acurrent running through an integrated circuit when a test signal isapplied to the integrated circuit, without preparing data of anintegrated circuit in no failure, as a reference, the method includingthe steps of (a) assuming that all integrated circuits under test definea under-test integrated circuit set, and testing each one of theintegrated circuits in the under-test integrated circuit set in aconventional manner, (b) removing integrated circuits having been judgedto be in failure in the step (a), from the under-test integrated circuitset, (c) measuring spectrum of a current supplied from a power sourceinto each one of the integrated circuits in the under-test integratedcircuit set, (d) calculating both a mean value and standard deviation ofthe spectrum for the under-test integrated circuit set, (e) judgingwhether an integrated circuit is in failure or in no failure, based onboth the mean value and the standard deviation of the spectrum, (f)removing integrated circuits having been judged to be in failure in thestep (e), from the under-test integrated circuit set, and (g) judgingthe under-test integrated circuit set to be in no failure.

It is preferable that the method further includes the step (h) ofnormalizing the spectrum, the step (h) being to be carried outsubsequently to the step (c).

It is preferable that the step (h) further includes the steps of (h1)summing up spectrum for all frequencies to have a total, and (h2)calculating a ratio of spectrum for each one of frequencies to thetotal.

It is preferable that the step (e) further includes the steps of (e1)calculating a gap between the spectrum and the mean value, (e2) dividingthe gap by the standard deviation, (e3) comparing a quotient obtained inthe step (e2) to a predetermined value, and (e4) judging an integratedcircuit to be in failure, if the quotient is greater than thepredetermined value, and judging an integrated circuit to be in nofailure, if the quotient is equal to or smaller than the predeterminedvalue.

There is further provided a method of detecting an integrated circuit infailure among integrated circuits, based on spectrum which is a resultof analyzing a frequency of a current running through an integratedcircuit when a test signal is applied to the integrated circuit, withoutpreparing data of an integrated circuit in no failure, as a reference,the method including the steps of (a) assuming that all integratedcircuits under test define a under-test integrated circuit set, andtesting each one of the integrated circuits in the under-test integratedcircuit set in a conventional manner, (b) removing integrated circuitshaving been judged to be in failure in the step (a), from the under-testintegrated circuit set, (c) measuring spectrum of a current suppliedfrom a power source into each one of the integrated circuits in theunder-test integrated circuit set, (d) calculating a mean value andstandard deviation of the spectrum for the under-test integrated circuitset, (e) checking whether the standard deviation is equal to or smallerthan a predetermined value, (f) removing an integrated circuit havingspecific spectrum determined based on the mean value, from theunder-test integrated circuit set, if the standard deviation is greaterthan the predetermined value, and repeating the steps (d), (e) and (f),and (g) judging the under-test integrated circuit set to be in nofailure, if the standard deviation has been judged to be equal to orsmaller than the predetermined value in the step (e).

It is preferable that the method further includes the step (h) ofnormalizing the spectrum, the step (h) being to be carried outsubsequently to the step (c).

It is preferable that the step (h) further includes the steps of (h1)summing up spectrum for all frequencies to have a total, and (h2)calculating a ratio of spectrum for each one of frequencies to thetotal.

It is preferable that the step (f) further includes the steps of (f1)calculating a gap between the spectrum and the mean value for each oneof frequencies, (f2) identifying an integrated circuit having a maximumgap among gaps calculated in the step (f1), and (f3) removing theintegrated circuit identified in the step (f2), from the under-testintegrated circuit set.

There is still further provided a method of detecting an integratedcircuit in failure among integrated circuits, based on spectrum which isa result of analyzing a frequency of a current running through anintegrated circuit when a test signal is applied to the integratedcircuit, without preparing data of an integrated circuit in no failure,as a reference, the method including the steps of (a) testing integratedcircuits to find an integrated circuit in no failure, (b) measuringspectrum of a current supplied from a power source into the integratedcircuit, (c) judging the integrated circuit to be in failure, (d)repeating the steps (a) to (c) until spectrum is measured for Nintegrated circuits wherein N is a predetermined integer, (e)calculating a mean value and standard deviation for each frequencieswith respect to the spectrum of the N integrated circuits, (f) judgingwhether the spectrum is abnormal or not, based on the mean value and thestandard deviation, (g) deleting data of spectrum having been judgedabnormal in the step (f), and repeating the steps (a) to (f), (h)defining the mean value and the standard deviation as a reference, (i)testing integrated circuits to find an integrated circuit in no failure,(j) measuring spectrum of a current supplied from a power source intothe integrated circuit, (k) judging whether the spectrum is abnormal ornot, based on the reference, and judging an integrated circuit to beeither in no failure if the spectrum is abnormal or in failure if thespectrum is not abnormal, (l) carrying out the steps (i) to (j) forintegrated circuits not tested yet, (m) defining integrated circuitshaving been judged to be in failure as integrated circuits not testedyet, and (n) repeating the steps (i) to (l).

It is preferable that the step (k) further includes the step of updatingthe reference, based on data of the spectrum.

It is preferable that the method further includes the step (o) ofnormalizing the spectrum, the step (o) being to be carried outsubsequently to at least one of the steps (b) and (j).

It is preferable that the step (o) includes the steps of (o1) summing upspectrum for all frequencies to have a total, and (o2) calculating aratio of spectrum for each one of frequencies to the total.

It is preferable that the method further includes the step (o) ofnormalizing the spectrum, the step (o) being to be carried outsubsequently to at least one of the steps (b) and (j).

It is preferable that the step (o) includes the steps of (o1) summing upspectrum for all frequencies to have a total, and (o2) calculating aratio of spectrum for each one of frequencies to the total.

It is preferable that the step (f) further includes the steps of (f1)calculating a gap between the spectrum and the mean value, (f2) dividingthe gap by the standard deviation, (f3) comparing a quotient obtained inthe step (f2) to a predetermined value, and (f4) judging the spectrum tobe abnormal, if the quotient is greater than the predetermined value,and judging the spectrum not to be abnormal, if the quotient is equal toor smaller than the predetermined value.

It is preferable that the spectrum is judged not abnormal if thespectrum is equal to or smaller than the reference, and is judgedabnormal if the spectrum is greater than the reference, in the step (k).

There is yet further provided a method of detecting an integratedcircuit in failure among integrated circuits, based on spectrum which isa result of analyzing a frequency of a current running through anintegrated circuit when a test signal is applied to the integratedcircuit, without preparing data of an integrated circuit in no failure,as a reference, the method including the steps of (a) measuring spectrumof some of integrated circuits among integrated circuits under test, tothereby establish a reference, and (b) comparing the rest of integratedcircuits among integrated circuits under test, to the reference tothereby judge whether each one of the rest of integrated circuits is infailure or not.

It is preferable that the method further includes the step of (c)judging whether the some of integrated circuits are in failure or not,based on the reference.

It is preferable that the method further includes the steps of (c)assuming that the some of integrated circuits are all in failure, and(d) judging again whether integrated circuits which have been judged tobe in failure are in failure or not, after all integrated circuits havebeen judged as to whether they are in failure or not.

In another aspect of the present invention, there is provided anapparatus for detecting an integrated circuit in failure amongintegrated circuits, based on spectrum which is a result of analyzing afrequency of a current running through an integrated circuit when a testsignal is applied to the integrated circuit, without preparing data ofan integrated circuit in no failure, as a reference, the apparatusincluding (a) a tester which tests an integrated circuit in aconventional manner as to whether the integrated circuit is in failureor not, (b) a spectrum measurement unit which measures spectrum of theintegrated circuit, (c) a first memory storing the spectrum therein, (d)a calculator calculating both a mean value and standard deviation ofspectrum of all integrated circuits under test, based on the spectrumstored in the first memory, and (e) a controller which judges whether anintegrated circuit is in failure or in no failure, based on both themean value and the standard deviation of the spectrum.

It is preferable that the controller judges whether an integratedcircuit is in failure or in no failure, based on comparison between avalue defined as G/SD and a threshold value, wherein G indicates a gapbetween the spectrum and the mean value, and SD indicates the standarddeviation.

It is preferable that the controller judges an integrated circuit to bein failure, if the value is greater than the threshold value, and judgesan integrated circuit to be in no failure, if the value is equal to orsmaller than the threshold value.

It is preferable that the apparatus further includes a second memory inwhich the threshold value is to be stored.

It is preferable that the controller judges that an integrated circuithaving a maximum G/SD is in failure, when the standard deviation isgreater than the threshold value.

It is preferable that the apparatus further includes a normalizer whichnormalizes the spectrum and replaces the previous spectrum with thenormalized spectrum.

There is further provided an apparatus for detecting an integratedcircuit in failure among integrated circuits, based on spectrum which isa result of analyzing a frequency of a current running through anintegrated circuit when a test signal is applied to the integratedcircuit, without preparing data of an integrated circuit in no failure,as a reference, the apparatus including (a) a tester which tests anintegrated circuit in a conventional manner as to whether the integratedcircuit is in failure or not, (b) a spectrum measurement unit whichmeasures spectrum of the integrated circuit, (c) a first memory storingthe spectrum therein, and (d) a controller which establishes areference, based on spectrum of the predetermined number of integratedcircuits under test, and judges whether an integrated circuit is infailure or in no failure, by comparing spectrum of each one of theintegrated circuits under test to the reference.

It is preferable that the controller updates the reference, based onspectrum of an integrated circuit having been judged to be in nofailure.

There is still further provided an apparatus for detecting an integratedcircuit in failure among integrated circuits, based on spectrum which isa result of analyzing a frequency of a current running through anintegrated circuit when a test signal is applied to the integratedcircuit, without preparing data of an integrated circuit in no failure,as a reference, the apparatus including (a) a logic tester which testsan integrated circuit in a conventional manner as to whether theintegrated circuit is in failure or not, (b) a spectrum measurement unitwhich measures spectrum of the integrated circuit, (c) a first memorystoring the spectrum therein, (d) a calculator calculating both a meanvalue and standard deviation of spectrum of all integrated circuitsunder test, for each of frequencies, based on the spectrum stored in thefirst memory, and (e) a controller which judges whether an integratedcircuit is in failure or in no failure, based on both the mean value andthe standard deviation of the spectrum.

There is yet further provided an apparatus for detecting an integratedcircuit in failure among integrated circuits, based on spectrum which isa result of analyzing a frequency of a current running through anintegrated circuit when a test signal is applied to the integratedcircuit, without preparing data of an integrated circuit in no failure,as a reference, the apparatus including (a) a logic tester which testsan integrated circuit in a conventional manner as to whether theintegrated circuit is in failure or not, (b) a spectrum measurement unitwhich measures spectrum of the integrated circuit, (c) a first memorystoring the spectrum therein, (d) a calculator calculating both a meanvalue and standard deviation of spectrum of all integrated circuitsunder test, for each of frequencies, based on the spectrum stored in thefirst memory, and (e) a controller which establishes a reference, basedon spectrum of the predetermined number of integrated circuits undertest, and judges whether an integrated circuit is in failure or in nofailure, by comparing spectrum of each one of the integrated circuitsunder test to the reference.

It is preferable that the apparatus further includes (f) a firstcontainer for containing therein integrated circuits not tested yet, (g)a second container for containing therein integrated circuits havingbeen judged to be in no failure, and (h) a third container forcontaining therein integrated circuits having been judged to be infailure.

It is preferable that the controller updates the reference, based onspectrum of an integrated circuit having been judged to be in nofailure.

In still another aspect of the present invention, there is provided arecording medium readable by a computer, storing a program therein forcausing a computer to carry out the above-mentioned method.

There is further provided a recording medium readable by a computer,storing a program therein for causing a computer to act as theabove-mentioned apparatus.

The advantages obtained by the aforementioned present invention will bedescribed hereinbelow.

As mentioned earlier, a method of detecting an integrated circuit infailure, based on spectrum of a power source current is accompanied witha problem that it is quite difficult to prepare a reference, that is,spectrum of a power source current of an integrated circuit having nofailures, because of difference in processing conditions in fabricationof integrated circuits. The inventor found out the fact that almost allintegrated circuits actually have no failures among integrated circuitshaving been judged to have no failures in accordance with a conventionalmethod, and that quite a small number of integrated circuits havingfailures could not be detected in accordance with a conventional method.Based on this discovery, the inventor herein suggests a method ofdetecting an integrated circuit in failure by analyzing spectrum of apower source current of all integrated circuits under test.

Specifically, integrated circuits are all tested in accordance with aconventional method to thereby have an under-test integrated circuit setcontaining integrated circuits having been judged to have no failures inaccordance with a conventional method. This under-test integratedcircuit set contains integrated circuits which have failures, but havenot been detected in accordance with a conventional manner, at a quitesmall rate, though.

Then, power source current spectrum is observed for each one ofintegrated circuits belonging to the under-test integrated circuit set,to thereby calculate a mean value and standard deviation. Then, a gapbetween spectrum and the mean value in each one of the integratedcircuits is standardized by the standard deviation to thereby quantifythe gap in the under-test integrated circuit set.

Though spectrum of integrated circuits having no failures are expectedto distribute in the vicinity of the mean value, spectrum of integratedcircuits having failures distribute much far away from the mean value.Accordingly, it would be possible to select integrated circuits havingno failures by removing integrated circuits having spectrum distributingfar away from the mean value, even without preparation of a reference,that is, data about spectrum of integrated circuits having no failures.

The above and other objects and advantageous features of the presentinvention will be made apparent from the following description made withreference to the accompanying drawings, in which like referencecharacters designate the same or similar parts throughout the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the apparatus in accordance with the firstembodiment.

FIG. 2 is a flow-chart showing an operation of the apparatus inaccordance with the first embodiment.

FIG. 3 is a block diagram of the apparatus in accordance with an exampleof the first embodiment.

FIG. 4 is a flow-chart showing an operation of the apparatus inaccordance with the example of the first embodiment.

FIG. 5 is a block diagram of the apparatus in accordance with the secondembodiment.

FIG. 6 is a flow-chart showing an operation of the apparatus inaccordance with the second embodiment.

FIG. 7 is a block diagram of the apparatus in accordance with an exampleof the second embodiment.

FIG. 8 is a flow-chart showing an operation of the apparatus inaccordance with the example of the second embodiment.

FIG. 9 is a block diagram of the apparatus in accordance with the thirdembodiment.

FIGS. 10 and 11 are flow-charts showing an operation of the apparatus inaccordance with the third embodiment.

FIG. 12 is a block diagram of the apparatus in accordance with anexample of the third embodiment.

FIGS. 13 and 14 are flow-charts showing an operation of the apparatus inaccordance with the example of the third embodiment.

FIG. 15 is a block diagram of the apparatus in accordance with thefourth embodiment.

FIGS. 16 and 17 are flow-charts showing an operation of the apparatus inaccordance with the fourth embodiment.

FIG. 18 is a block diagram of the apparatus in accordance with anexample of the fourth embodiment.

FIGS. 19 and 20 are flow-charts showing an operation of the apparatus inaccordance with the example of the fourth embodiment.

FIG. 21 is a block diagram of the apparatus in accordance with the fifthembodiment.

FIG. 22 is a flow-chart showing an operation of the apparatus inaccordance with the fifth embodiment.

FIG. 23 is a block diagram of the apparatus in accordance with anexample of the fifth embodiment.

FIG. 24 is a flow-chart showing an operation of the apparatus inaccordance with the example of the fifth embodiment.

FIG. 25 is a block diagram of the apparatus in accordance with the sixthembodiment.

FIG. 26 is a flow-chart showing an operation of the apparatus inaccordance with the sixth embodiment.

FIG. 27 is a block diagram of the apparatus in accordance with anexample of the sixth embodiment.

FIG. 28 is a flow-chart showing an operation of the apparatus inaccordance with the example of the sixth embodiment.

FIG. 29 is a block diagram of the apparatus in accordance with theseventh embodiment.

FIGS. 30 and 31 are flow-charts showing an operation of the apparatus inaccordance with the seventh embodiment.

FIG. 32 is a block diagram of the apparatus in accordance with anexample of the seventh embodiment.

FIGS. 33 and 34 are flow-charts showing an operation of the apparatus inaccordance with the example of the seventh embodiment.

FIG. 35 is a block diagram of the apparatus in accordance with theeighth embodiment.

FIGS. 36 and 37 are flow-charts showing an operation of the apparatus inaccordance with the eighth embodiment.

FIG. 38 is a block diagram of the apparatus in accordance with anexample of the eighth embodiment.

FIGS. 39 and 40 are flow-charts showing an operation of the apparatus inaccordance with the example of the eighth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments in accordance with the present invention will beexplained hereinbelow with reference to drawings.

[First Embodiment]

FIG. 1 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with the first embodiment. The illustrated apparatus iscomprised of a tester 1, an under-test integrated circuit set 2, aspectrum measurement unit 3, a main controller 4, a first memory 7, asecond memory 5, and a calculator 6.

The under-test integrated circuit set 2 contains a plurality of the sameintegrated circuits to be tested as to whether they are in failure ornot. The tester 1 is controlled by the main controller 4, and tests eachone of integrated circuits in the under-test integrated circuit set 2 inaccordance with a conventional method as to whether each one ofintegrated circuits is in failure or not. For instance, the tester 1tests integrated circuits in accordance with the method mentioned in“The Electrical Handbook”, R. C. Dorf, 1993, pp. 1808-1816.

The test results are transmitted to the first memory 7 through the maincontroller 4, and are stored in the first memory 7. The spectrummeasurement unit 3 is controlled by the main controller 4. The spectrummeasurement unit 3 applies a test signal to each one of integratedcircuits in the under-test integrated circuit set 2, observes a powersource current running through the integrated circuit, and analyzes afrequency of the current. Power source current spectrum obtained byanalysis of a frequency is stored in the first memory 7 through the maincontroller 4.

The power source current spectrum is observed by the spectrummeasurement unit 3 only for integrated circuits having been judged tohave no failures by the tester 1. On receipt of an instructiontransmitted from the main controller 4, the calculator 6 judges whethereach one of integrated circuits in the under-test integrated circuit setis in failure or not, based on both data about power source currentspectrum, stored in the first memory 7, and data indicative of apredetermined value, stored in the second memory 5, and outputs theresults of judgement.

FIG. 2 is a flow-chart showing an operation of the apparatus inaccordance with the first embodiment. Herein, the under-test integratedcircuit set 2 containing a plurality of the same integrated circuits tobe tested is indicated with “A”. At this stage, the integrated circuitset A is identical with the under-test integrated circuit set 2.

First, integrated circuits in the integrated circuit set A are tested bythe tester 1 as to whether they are in failure or not in accordance withconventional tests such as a performance test or a direct current test,in step S101.

The results of the test are transmitted to and stored in the firstmemory 7. At the same time, integrated circuits having been judged to bein failure by the tester 1 are removed from the integrated circuit setA, in step S102.

The spectrum measurement unit 3 applies a test signal to each one ofintegrated circuits in the integrated circuit set A, that is, each oneof the integrated circuits having been judged to be in no failure amongthe under-test integrated circuit set 2 in step S101, observes a powersource current running through each one of the integrated circuits, andanalyzes a frequency of the observed current. Spectrum of a power sourcecurrent, obtained as a result of analysis of the frequency, istransmitted to and stored in the first memory 7, in step S103.

Then, the calculator 6 calculates a mean value and standard deviationfor each one of frequencies of the power source current spectrum of theintegrated circuits in the integrated circuit set A, based on thespectrum of the integrated circuits in the integrated circuit set A,stored in the first memory 7, in step S104.

In addition, the calculator 6 calculates G/SD for each one of theintegrated circuits for each one of frequencies wherein G indicates adifference between the spectrum of each one of integrated circuits inthe integrated circuit set A and the mean value, and SD indicates thestandard deviation having been calculated in step S104. If the thuscalculated G/SD is greater than the predetermined value stored in thesecond memory 5, the calculator 6 judges that an integrated circuithaving such G/SD is in failure, in step S105.

Then, it is judged in step S106 whether there has been found anintegrated circuit in failure in the integrated circuit set A.

If there has been found an integrated circuit having failures (YES instep S106), such an integrated circuit is removed from the integratedcircuit set A, in step S107, and steps S104 to S106 are repeated.

If there has not been found an integrated circuit having failures (NO instep S106), all the integrated circuits in the integrated circuit set Aare judged to be in no failure, in step S108.

The above-mentioned operation may be described as a control program andstored in a recording medium such as a floppy disc or ROM equipped withthe main controller 4. By carrying out the control program in the maincontroller 4, the above-mentioned operation can be repeated.

Hereinbelow are explained advantages provided by the above-mentionedfirst embodiment.

When an integrated circuit is tested as to whether it is in failure ornot, in accordance with a conventional method, the tested integratedcircuit may have any failure, even if the integrated circuit is judgedto be in no failure. In other words, it is not always possible to detectall failures in an integrated circuit in accordance with a conventionalmethod. This means that a conventional method can detect merely about95% of possible failures.

This is because ability of detecting failures is limited to practicalone on the ground that if all failures in an integrated circuit are tobe detected, it would take much time and cost.

In addition, there have been increased failure modes which could not begrouped in conventional failure models, as an integrated circuit hasbeen fabricated in a smaller size, at a higher speed, and in higherintegration. Such failure modes cannot be detected in accordance withconventional methods.

Thus, an integrated circuit often improperly operates due to failureswhich cannot be detected by conventional methods. It is quite importantto detect failures as much as possible. In the apparatus in accordancewith the first embodiment, data about a power source current is used inorder to detect a failure in an integrated circuit. Namely, whereas theconventional methods use data about a voltage for detecting failures,the apparatus in accordance with the first embodiment uses data about apower source current to thereby make it possible to detect failureswhich could not be detected by the conventional methods.

However, since a power source current is an analog value, and is muchinfluenced by processing conditions in fabrication of an integratedcircuit, it would be necessary to prepare data about a power sourcecurrent of an integrated circuit having no failures. It is quitedifficult to prepare such data as a reference.

Such data as a reference can be obtained by carrying out simulation inwhich a test signal is applied to an integrated circuit. However, itwould take much time to carry out such simulation for each of integratedcircuits.

When a plurality of integrated circuits are tested in accordance with aconventional method as to whether they are in failure or not, a majorityof integrated circuits having been judged to be in no failure hasactually no failures, and quite a minority of integrated circuits has afailure or failures. Accordingly, it is considered that almost allspectrum of a power source current of integrated circuits having beenjudged to be in no failure in accordance with a conventional methodexhibit almost the same value, and only a small number of integratedcircuits having a failure exhibits abnormal spectrum of a power sourcecurrent.

Thus, it is possible to identify integrated circuits having no failuresamong a plurality of integrated circuits without data about spectrum ofa power source current of an integrated circuit having no failures, byobserving spectrum of a power source current of integrated circuitshaving been judged to be in no failure in accordance with a conventionalmethod, and judging that integrated circuits exhibiting power sourcecurrent spectrum different from power source current spectrum exhibitedby a majority of integrated circuits among tested integrated circuitsare in failure.

In the above-mentioned first embodiment, integrated circuits exhibitingspectrum other than spectrum exhibited by a majority of integratedcircuits are identified as integrated circuits having spectrum which hasa great difference from a mean value. Specifically, a difference betweenspectrum of each one of integrated circuits and a mean value of spectrumin each of frequencies of the power source current spectrum is dividedby standard deviation. If the thus calculated quotient is greater than apredetermined value, an integrated circuit associated with the spectrumis judged to be in failure.

By repeating the above-mentioned calculation, the mean value andstandard deviation of the power source current spectrum are updated.Based on the thus updated mean value and standard deviation, anintegrated circuit exhibiting power source current spectrum greater thana predetermined value is judged to be in failure and removed. At thetime when no integrated circuits are judged to be in failure, it isjudged that all of tested integrated circuits are in no failure.

As mentioned so far, the first embodiment makes it possible to select amajority of integrated circuits having no failures from a minority ofintegrated circuits having failures.

Hereinbelow is explained an example of the apparatus in accordance withthe first embodiment.

FIG. 3 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with the example of the first embodiment, and FIG. 4 is aflow-chart showing an operation of the apparatus illustrated in FIG. 3.

The illustrated apparatus is comprised of a logic tester 101, anunder-test integrated circuit set 102, a spectrum measurement unit 103,a main controller 104, a first memory 107, a second memory 105, and acalculator 106.

The under-test integrated circuit set 102 contains a plurality of thesame integrated circuits to be tested as to whether they are in failureor not. The tester 101 is controlled by the main controller 104, andtests each one of integrated circuits in the under-test integratedcircuit set 102 in accordance with a conventional test such as afunction test or DC test, as to whether each one of integrated circuitsis in failure or not, in step S1101. Herein, a function test is a testby which each one of integrated circuits is tested as to whether it cansatisfactorily accomplish expected performances. The function test iscarried out by applying a test voltage signal to an integrated circuitthrough an input terminal thereof, and observing fluctuation of avoltage at an output terminal. DE test is a test by which each one ofintegrated circuits is tested as to whether input and outputcharacteristic of each one of integrated circuits meets withpredetermined characteristic.

The results of the test carried out by the logic tester 101 aretransmitted to in the first memory 107, and then, integrated circuitshaving been judged to be in no failure by the logic tester 101 arestored in the first memory 107 as an integrated circuit set A, in stepS1102.

Then, the spectrum measurement unit 103 applies a test signal to eachone of integrated circuits in the integrated circuit set A, observes apower source current running through each one of the integratedcircuits, and analyzes a frequency of the observed power source current.Spectrum of a power source current, obtained as a result of analysis ofthe frequency, is transmitted to and stored in the first memory 107, instep S1103.

Then, the calculator 106 calculates a mean value and standard deviationfor each one of frequencies of the power source current spectrum of theintegrated circuits in the integrated circuit set A, based on thespectrum of the integrated circuits in the integrated circuit set A,stored in the first memory 107, in step S1104.

The calculator 106 calculates G/SD for each one of the integratedcircuits for each one of frequencies wherein G indicates a differencebetween the spectrum of each one of integrated circuits in theintegrated circuit set A and the mean value, and SD indicates thestandard deviation having been calculated in step S1104. If the thuscalculated G/SD is greater than a predetermined value stored in thesecond memory 105, the calculator 106 judges that an integrated circuithaving such G/SD is in failure, in step S1105.

Then, it is judged in step S1106 whether there has been found anintegrated circuit in failure in the integrated circuit set A.

If there has been found an integrated circuit having failures (YES instep S1106), such an integrated circuit is removed from the integratedcircuit set A in step S1107, and steps S1104 to S1106 are repeated.

Steps S1104 to S1106 are repeated until there is no integrated circuitjudged to be in failure. Thus, if there has not been found an integratedcircuit having failures (NO in step S1106), all the integrated circuitsin the integrated circuit set A are judged to be in no failure, in stepS1108.

The above-mentioned operation may be described as a control program andstored in a recording medium such as a floppy disc or ROM equipped withthe main controller 104. By carrying out the control program in the maincontroller 104, the above-mentioned operation can be repeated.

[Second Embodiment]

FIG. 5 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with the second embodiment. The illustrated apparatus iscomprised of a tester 1, an under-test integrated circuit set 2, aspectrum measurement unit 3, a main controller 4 a, a first memory 7, asecond memory 5, and a calculator 6.

In comparison with the apparatus in accordance with the firstembodiment, the apparatus in accordance with the second embodiment isdesigned to include the main controller 4 a in place of the maincontroller 4. The main controller 4 a has different functions from thoseof the main controller 4.

FIG. 6 is a flow-chart showing an operation of the apparatus inaccordance with the second embodiment. Operation to be carried out insteps S201, S202, S203 and S204 in FIG. 6 are the same as operation tobe carried out in steps S101, S102, S103 and S104 in FIG. 2. Hence,explanation about steps S201, S202, S203 and S204 is omitted.

The calculator 6 calculates a mean value and standard deviation for eachone of frequencies of the power source current spectrum of integratedcircuits in the integrated circuit set A, based on the spectrum of theintegrated circuits in the integrated circuit set A, stored in the firstmemory 7, in step S204.

Then, it is judged whether the standard deviation is greater than apredetermined value stored in the second memory 5, in step S205. Thisjudgement is carried out for each one of frequencies of the power sourcecurrent spectrum.

If the standard deviation is greater than the predetermined value in acertain frequency (YES in step S205), an integrated circuit having amaximum gap among gaps between spectrum of each one of the integratedcircuits and the mean value of the spectrum of all the integratedcircuits in the frequency is removed from the integrated circuit set A,in step S206.

Then, steps S204 and S205 are repeated until the standard deviation isequal to or smaller than the predetermined value in each one of thefrequencies of the power source current. Thus, when the standarddeviation becomes equal to or smaller than the predetermined value ineach one of the frequencies of the power source current (NO in stepS205), all the integrated circuits in the integrated circuit set A arejudged to be in no failure, in step S207.

The above-mentioned operation may be described as a control program andstored in a recording medium such as a floppy disc or ROM equipped withthe main controller 4 a. By carrying out the control program in the maincontroller 4 a, the above-mentioned operation can be repeated.

Hereinbelow is explained advantages obtained by the above-mentionedsecond embodiment.

Almost all integrated circuits judged to be in no failure in accordancewith a conventional test actually have no failures. If a test signal isapplied to integrated circuits judged to be in no failure, a currentbehaves in the almost same manner in those integrated circuits, andhence, those integrated circuits have almost the same power sourcecurrent spectrum.

Dispersion in power source current spectrum is caused by fluctuation inprocessing conditions in fabrication integrated circuits. Since suchfluctuation can be predicted in advance, dispersion in power sourcecurrent spectrum of integrated circuits judged to be in no failure canalso be predicted. Dispersion in power source current spectrum can beindicated with standard deviation. Hence, in the second embodiment,degree of dispersion in power source current spectrum of integratedcircuits judged to be in no failure is indicated with standarddeviation, and is compared to a predetermined value.

Hence, if the integrated circuit set A comprised of integrated circuitshaving been judged to be in no failure in accordance with a conventionaltest contains integrated circuits having failures, the standarddeviation of the power source current spectrum would be greater than apredetermined value. Thus, if the standard deviation is over apredetermined value, it is considered that an integrated circuit havinga maximum gap among gaps between power source current spectrum of eachone of integrated circuits and a mean value of power source currentspectrum of all integrated circuits has any failures. By removing suchan integrated circuit, there is obtained the integrated circuit set Acomprised only of integrated circuits

In addition, the apparatus in accordance with the second embodiment alsohas the same advantages as those provided by the apparatus in accordancewith the first embodiment.

Hereinbelow is explained an operation of the apparatus in accordancewith the second embodiment with reference to a specific example.

FIG. 7 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with the example of the second embodiment.

The illustrated apparatus is comprised of a logic tester 101, anunder-test integrated circuit set 102, a spectrum measurement unit 103,a main controller 104 a, a first memory 107, a second memory 105, and acalculator 106.

In comparison with the apparatus in accordance with the example of thefirst embodiment, illustrated in FIG. 3, the apparatus in accordancewith the example of the second embodiment is designed to include themain controller 104 a in place of the main controller 104. The maincontroller 104 a has different functions from those of the maincontroller 104.

FIG. 8 is a flow-chart showing an operation of the apparatus inaccordance with the example. Operation to be carried out in steps S1201,S1202, S1203 and S1204 in FIG. 8 are the same as operation to be carriedout in steps S1101, S1102, S1103 and S1104 in FIG. 4. Hence, explanationabout steps S1201, S1202, S1203 and S1204 is omitted.

The calculator 6 calculates standard deviation for each one offrequencies of the power source current spectrum of integrated circuitsin the integrated circuit set A, based on the spectrum of the integratedcircuits in the integrated circuit set A, stored in the first memory107, in step S1204.

Then, it is judged in the main controller 104 a whether the standarddeviation is greater than a predetermined value stored in the secondmemory 105, in step S1205. This judgement is carried out for each one offrequencies of the power source current spectrum.

If the standard deviation is greater than the predetermined value in acertain frequency (YES in step S1205), an integrated circuit having amaximum gap among gaps between spectrum of each one of integratedcircuits and the mean value of the spectrum of all the integratedcircuits in the frequency is removed from the integrated circuit set A,in step S1206.

Then, steps S1204 and S1205 are repeated until the standard deviation isequal to or smaller than the predetermined value in each one of thefrequencies of the power source current. Thus, when the standarddeviation becomes equal to or smaller than the predetermined value ineach one of the frequencies of the power source current (NO in stepS1205), all the integrated circuits in the integrated circuit set A arejudged to be in no failure, in step S1207.

The above-mentioned operation may be described as a control program andstored in a recording medium such as a floppy disc or ROM equipped withthe main controller 104 a. By carrying out the control program in themain controller 104 a, the above-mentioned operation can be repeated.

[Third Embodiment]

FIG. 9 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with the third embodiment. The illustrated apparatus iscomprised of a tester 1, an under-test integrated circuit set 12, aspectrum measurement unit 3, a main controller 4 b, a first memory 7, asecond memory 5, a calculator 6, a first set 9 comprised of integratedcircuits having been judged to have no failures, and a second set 10comprised of integrated circuits judged to have failures.

The under-test integrated circuit set 12 is comprised of a plurality ofthe same integrated circuits not tested yet. An integrated circuit 8 isselected one by one from the under-test integrated circuit set 12, andis tested by the tester 1. If the integrated circuit 8 is judged to haveno failures, the integrated circuit 8 is introduced into the first set9. In contrast, if the integrated circuit 8 is judged to have failures,the integrated circuit 8 is introduced into the second set 10.

The tester 1 is controlled by the main controller 4 b, and tests theintegrated circuit 8 in accordance with conventional tests as to whetherthe integrated circuit 8 is in failure or not.

The test results are transmitted to the first memory 7 through the maincontroller 4 b, and are stored in the first memory 7. The spectrummeasurement unit 3 is controlled by the main controller 4 b. Thespectrum measurement unit 3 applies a test signal to the integratedcircuit 8, observes a power source current running through theintegrated circuit 8, and analyzes a frequency of the power sourcecurrent. Power source current spectrum obtained by analysis of afrequency is stored in the first memory 7 through the main controller 4b.

On receipt of an instruction transmitted from the main controller 4 b,the calculator 6 judges whether the integrated circuit 8 in failure ornot, based on both data about power source current spectrum of theintegrated circuit 8, stored in the first memory 7, and data indicativeof a predetermined value, stored in the second memory 5.

FIGS. 10 and 11 are flow-charts showing an operation of the apparatus inaccordance with the third embodiment.

As mentioned earlier, the under-test integrated circuit set 12 iscomprised of integrated circuits not yet judged as to whether they arein failure or not. An integrated circuit is selected one by one from theunder-test integrated circuit set 12, and the thus selected integratedcircuit 8 is tested by the tester 1 in accordance with conventionaltests, in step S301.

Then, it is judged in step S302 that the tested integrated circuit 8 iswhether in failure or not.

If the tested integrated circuit 8 is judged to be in failure (YES instep S302), the tested integrated circuit 8 is introduced into thesecond set 10 in step S304. Then, steps S301 and S302 are repeated.

In contrast, if the tested integrated circuit 8 is judged to be in nofailure (NO in step S302), the spectrum measurement unit 3 applies atest signal to the integrated circuit 8, observes a power source currentrunning through the integrated circuit, and analyzes a frequency of theobserved power source current, in step S303. Spectrum of the powersource current obtained as a result of analysis of the frequency of theobserved current is transmitted to and stored in the first memory 7.

Then, the integrated circuit 8 is introduced into the second set 10, instep S305.

Then, it is judged in step S306 whether the predetermined number N ofthe integrated circuits 8 have already been judged to be in no failure,in step S306.

If the number of the integrated circuits 8 having been judged to be inno failure is smaller than N (NO in step S306), steps S301, S302, S303and S305 are repeated.

In contrast, if the number of the integrated circuits 8 having beenjudged to be in no failure is equal to N (YES in step S306), a meanvalue and standard deviation are calculated by the calculator 6 for eachone of the frequencies of the power source current, based on the powersource current spectrum of all the integrated circuits, stored in thefirst memory 7, in step S307.

Then, the calculator 6 calculates a value defined as G/SD wherein Gindicates a difference between the mean value of spectrum of all theintegrated circuits and spectrum of each one of the integrated circuits,and SD indicates the standard deviation, in step S308. This calculationis carried out for each one of the frequencies of the power sourcecurrent.

Then, it is judged in step S309 whether the value G/SD is greater than apredetermined value stored in the second memory 5.

If the value G/SD is greater than the predetermined value (YES in stepS309), the integrated circuit having the value G/SD is judged to be infailure, and data about power source current spectrum of the integratedcircuit is removed from the first memory 7, in step S311. Then, stepsS301, S302, S305, S306, S307, S309 are repeated.

If the value G/SD is equal to or smaller than the predetermined value(NO in step S309), the mean value and the standard deviation aredetermined as a reference, and this reference is stored in the firstmemory 7, in step S310.

Then, a next integrated circuit 8 is selected from the under-testintegrated circuit set 12, and is tested by the tester 1 as to whetherit is in failure or not in accordance with conventional tests, in stepS312.

Then, it is judged in step S313 that the tested integrated circuit 8 iswhether in failure or not.

If the tested integrated circuit 8 is judged to be in failure (YES instep S313), the tested integrated circuit 8 is introduced into thesecond set 10 in step S314. Then, steps S312 and S313 are repeated.

In contrast, if the tested integrated circuit 8 is judged to be in nofailure (NO in step S313), the spectrum measurement unit 3 applies atest signal to the integrated circuit 8, observes a power source currentrunning through the integrated circuit, and analyzes a frequency of theobserved power source current, to thereby obtain spectrum of the powersource current as a result of analysis of the frequency of the observedcurrent, in step S315.

Then, the calculator 6 evaluates the thus obtained spectrum incomparison with the reference stored in the first memory 7, as follows.

First, there is calculated a value defined as G/SD wherein G indicates adifference between a mean value of the reference and the power sourcecurrent spectrum, and SD indicates standard deviation of the reference,in step S316. Then, it is judged in step S317 whether the value G/SD isequal to or smaller than a predetermined value stored in the secondmemory 5 in each one of the frequencies of the power source current.

If the value G/SD is equal to or smaller than the predetermined value(YES in step S317), an integrated circuit having the value G/SD isjudged to be in no failure, in step S318. Then, the integrated circuitis introduced into the first set 9.

In contrast, if the value G/SD is greater than the predetermined value(NO in step S317), an integrated circuit having the value G/SD is judgedto be in failure, in step S319. Then, the integrated circuit isintroduced into the second set 10.

Then, it is checked in step S320 whether the under-test integratedcircuit set 12 is not empty, that is, the under-test integrated circuitset 12 still contains integrated circuits not yet tested.

If the under-test integrated circuit set 12 still contains integratedcircuits not yet tested (YES in step S320), steps S312, S313, S315, S316and S317 are repeatedly carried out.

If the under-test integrated circuit set 12 is empty, that is, theunder-test integrated circuit set 12 does no longer contain integratedcircuits not tested (NO in step S320), the integrated circuits in thesecond set 10 are tested again in step S321. Specifically, theintegrated circuits contained in the second set 10 are all transferredinto the under-test integrated circuit set 12. As a result, the secondset 10 becomes empty.

Then, a next integrated circuit 8 is selected from the under-testintegrated circuit set 12, and is tested by the tester 1 as to whetherit is in failure or not in accordance with conventional tests, in stepS322.

Then, it is judged in step S323 that the tested integrated circuit 8 iswhether in failure or not.

If the tested integrated circuit 8 is judged to be in failure (YES instep S323), the tested integrated circuit 8 is introduced into thesecond set 10 in step S324. Then, steps S322 and S323 are repeated.

In contrast, if the tested integrated circuit 8 is judged to be in nofailure (NO in step S323), the spectrum measurement unit 3 applies atest signal to the integrated circuit 8, observes a power source currentrunning through the integrated circuit, and analyzes a frequency of theobserved power source current, to thereby obtain spectrum of the powersource current as a result of analysis of the frequency of the observedcurrent, in step S325.

Then, the calculator 6 evaluates the thus obtained spectrum incomparison with the reference stored in the first memory 7, as follows.

First, there is calculated a value defined as G/SD wherein G indicates adifference between a mean value of the reference and the power sourcecurrent spectrum, and SD indicates standard deviation of the reference,in step S326. Then, it is judged in step S327 whether the value G/SD isequal to or smaller than a predetermined value stored in the secondmemory 5 in each one of the frequencies of the power source current.

If the value G/SD is equal to or smaller than the predetermined value(YES in step S327), an integrated circuit having the value G/SD isjudged to be in no failure, in step S328. Then, the integrated circuitis introduced into the first set 9.

In contrast, if the value G/SD is greater than the predetermined value(NO in step S327), an integrated circuit having the value G/SD is judgedto be in failure, in step S329. Then, the integrated circuit isintroduced into the second set 10.

Then, it is checked in step S330 whether the under-test integratedcircuit set 12 is not empty, that is, the under-test integrated circuitset 12 still contains integrated circuits not yet tested.

If the under-test integrated circuit set 12 still contains integratedcircuits not yet tested (YES in step S330), steps S322, S323, S325, S326and S327 are repeatedly carried out.

If the under-test integrated circuit set 12 is empty, that is, theunder-test integrated circuit set 12 does no longer contain integratedcircuits not tested (NO in step S330), the test is ended.

The above-mentioned operation may be described as a control program andstored in a recording medium such as a floppy disc or ROM equipped withthe main controller 4 b. By carrying out the control program in the maincontroller 4 b, the above-mentioned operation can be repeated.

Hereinbelow are explained advantages obtained by the above-mentionedthird embodiment.

In a conventional method of identifying an integrated circuit in failureamong a plurality of integrated circuits, a reference is in advanceprepared. Hence, each one of integrated circuits is judged whether it isin failure or not by comparing it to the reference.

However, it is generally difficult for the above-mentioned reasons toprepare an accurate reference. Hence, in accordance with the thirdembodiment, integrated circuits are all tested once. Then, there isestablished a reference, based on the result of the test. Then, allintegrated circuits are judged whether they are in failure or not bycomparing them to the thus established reference.

In the above-mentioned first and second embodiments, each one ofintegrated circuits to be tested is numbered, and thus, data about powersource current spectrum is stored in the first memory 7 in associationwith each one of the integrated circuits. Hence, all the integratedcircuits are judged whether they are in failure or not after data ofpower source current spectrum of all the integrated circuits has beencollected, and integrated circuits in failure can be identified bydetecting abnormal spectrum.

However, in accordance with the first and second embodiments, each oneof integrated circuits to be tested has to be numbered and correlatedwith power source current spectrum, which might take extra time to testall the integrated circuits.

Hence, in accordance with the third embodiment, power source currentspectrum is observed in a certain number of integrated circuits only forthe purpose of establishing a reference. After power source currentspectrum has been observed in a number of integrated circuits sufficientto establish a reference, the rest of integrated circuits are judged asto whether they are in failure or not, based on the thus establishedreference.

However, the integrated circuits used only for establishing a referenceare not yet judged as to whether they are in failure or not. Hence, theyare preferably judged as to whether they are in failure or not, based onthe established reference. To this end, they are provisionallydetermined to be in failure when a reference is established. Then, afterintegrated circuits have been all judged as to whether they are infailure or not, integrated circuits having been judged to be in failureare judged again as to whether they are in failure or not. Thus, it ispossible to identify all integrated circuits having no failures, and toestablish a reference with a small number of steps.

In place of judging integrated circuits used for establishing areference, to be in failure, they might be provisionally determined tobe in semi-failure to distinguish from integrated circuits judged to bein failure. When all integrated circuits are judged again as to whetherthey are in failure or not after a reference has been established, onlythose integrated circuits in semi-failure are judged as to whether theyare in failure or not. As a result, it is no longer necessary to judgeagain whether integrated circuits having been once judged to be infailure, are in failure or not.

Hereinbelow is explained an operation of the third embodiment withreference to an example.

FIG. 12 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with an example of the third embodiment. The illustratedapparatus is comprised of a logic tester 101, a spectrum measurementunit 103, a main controller 104 b, a first memory 107, a second memory105, a calculator 106, a first container 109 containing integratedcircuits having been judged to have no failures, a second container 110containing integrated circuits judged to have failures, and a thirdcontainer 112 containing integrated circuits to be tested.

FIGS. 13 and 14 are flow-charts showing an operation of the apparatus inaccordance with the example of the third embodiment.

As mentioned earlier, the third container 112 contains all of integratedcircuits which are to be judged as to whether they are in failure ornot. An integrated circuit is selected one by one from the thirdcontainer 112, and the thus selected integrated circuit 108 is tested bythe tester 101 in accordance with conventional tests such as a functiontest and DC test, in step S1301.

Then, it is judged in step S1302 that the tested integrated circuit 8 iswhether in failure or not.

If the tested integrated circuit 108 is judged to be in failure (YES instep S1302), the tested integrated circuit 108 is introduced into thesecond container 110 in step S1304. Then, steps S1301 and S1302 arerepeated.

In contrast, if the tested integrated circuit 108 is judged to be in nofailure (NO in step S1302), the spectrum measurement unit 103 applies atest signal to the integrated circuit 108, observes a power sourcecurrent running through the integrated circuit, and analyzes a frequencyof the observed power source current, in step S1303. Spectrum of thepower source current obtained as a result of analysis of the frequencyof the observed current is transmitted to and stored in the first memory107.

Then, the integrated circuit 108 having been judged to be in no failureis introduced into the second container 110, in step S1305.

Then, it is judged in step S1306 whether the predetermined number N ofthe integrated circuits 108 have already been judged to be in nofailure, in step S1306.

If the number of the integrated circuits 108 having been judged to be inno failure is smaller than N (NO in step S1306), steps S1301, S1302,S1303 and S1305 are repeated.

In contrast, if the number of the integrated circuits 8 having beenjudged to be in no failure is equal to N (YES in step S1306), a meanvalue and standard deviation are calculated by the calculator 106 foreach one of the frequencies of the power source current, based on thepower source current spectrum of all the integrated circuits, stored inthe first memory 107, in step S1307.

Then, the calculator 106 calculates a value defined as G/SD wherein Gindicates a difference between the mean value of spectrum of all theintegrated circuits and spectrum of each one of the integrated circuits,and SD indicates the standard deviation, in step S1308. This calculationis carried out for each one of the frequencies of the power sourcecurrent.

Then, it is judged in step S1309 whether the value G/SD is greater thana predetermined value stored in the second memory 105.

If the value G/SD is greater than the predetermined value (YES in stepS1309), the integrated circuit 108 having the value G/SD is judged to bein failure, and data about power source current spectrum of theintegrated circuit is removed from the first memory 107, in step S1311.Then, steps S1301, S1302, S1305, S1306, S1307, S1309 are repeated.

If the value G/SD is equal to or smaller than the predetermined value(NO in step S1309), the mean value and the standard deviation aredetermined as a reference, and this reference is stored in the firstmemory 107, in step S1310.

Then, a next integrated circuit 108 is selected from the third container112, and is tested by the logic tester 101 as to whether it is infailure or not in accordance with conventional tests such as a functiontest and DC test, in step S1312.

Then, it is judged in step S1313 that the tested integrated circuit 108is whether in failure or not.

If the tested integrated circuit 108 is judged to be in failure (YES instep S1313), the tested integrated circuit 108 is introduced into thesecond container 110 in step S1314. Then, steps S1312 and S1313 arerepeated.

In contrast, if the tested integrated circuit 108 is judged to be in nofailure (NO in step S1313), the spectrum measurement unit 103 applies atest signal to the integrated circuit 108, observes a power sourcecurrent running through the integrated circuit, and analyzes a frequencyof the observed power source current, to thereby obtain spectrum of thepower source current as a result of analysis of the frequency of theobserved current, in step S1315.

Then, the calculator 106 evaluates the thus obtained spectrum incomparison with the reference stored in the first memory 107, asfollows.

First, there is calculated a value defined as G/SD wherein G indicates adifference between a mean value of the reference and the power sourcecurrent spectrum, and SD indicates standard deviation of the reference,in step S1316. Then, it is judged in step S1317 whether the value G/SDis equal to or smaller than a predetermined value stored in the secondmemory 105 in each one of the frequencies of the power source current.

If the value G/SD is equal to or smaller than the predetermined value(YES in step S1317), an integrated circuit having the value G/SD isjudged to be in no failure, in step S1318. Then, the integrated circuitis introduced into the first container 109.

In contrast, if the value G/SD is greater than the predetermined value(NO in step S1317), an integrated circuit having the value G/SD isjudged to be in failure, in step S1319. Then, the integrated circuit isintroduced into the second container 110.

Then, it is checked in step S1320 whether the third container 112 stillcontains integrated circuits not yet tested.

If the third container 112 still contains integrated circuits not yettested (YES in step S1320), steps S1312, S1313, S1315, S1316 and S1317are repeatedly carried out.

If the third container 112 does no longer contain integrated circuitsnot tested (NO in step S1320), the integrated circuits in the secondcontainer 110 are tested again in step S1321. Specifically, theintegrated circuits contained in the second container 110 are alltransferred into the third container 112.

Then, a next integrated circuit 108 is selected from the third container112, and is tested by the logic tester 101 as to whether it is infailure or not in accordance with conventional tests such as a functiontest and DC test, in step S1322.

Then, it is judged in step S1323 that the tested integrated circuit 108is whether in failure or not.

If the tested integrated circuit 108 is judged to be in failure (YES instep S1323), the tested integrated circuit 108 is introduced into thesecond container 110 in step S1324. Then, steps S1322 and S1323 arerepeated.

In contrast, if the tested integrated circuit 108 is judged to be in nofailure (NO in step S1323), the spectrum measurement unit 103 applies atest signal to the integrated circuit 108, observes a power sourcecurrent running through the integrated circuit, and analyzes a frequencyof the observed power source current, to thereby obtain spectrum of thepower source current as a result of analysis of the frequency of theobserved current, in step S1325.

Then, the calculator 106 evaluates the thus obtained spectrum incomparison with the reference stored in the first memory 107, asfollows.

First, there is calculated a value defined as G/SD wherein G indicates adifference between a mean value of the reference and the power sourcecurrent spectrum, and SD indicates standard deviation of the reference,in step S1326. Then, it is judged in step S1327 whether the value G/SDis equal to or smaller than a predetermined value stored in the secondmemory 105 in each one of the frequencies of the power source current.

If the value G/SD is equal to or smaller than the predetermined value(YES in step S1327), the integrated circuit having the value G/SD isjudged to be in no failure, in step S1328. Then, the integrated circuitis introduced into the first container 109.

In contrast, if the value G/SD is greater than the predetermined value(NO in step S1327), an integrated circuit having the value G/SD isjudged to be in failure, in step S1329. Then, the integrated circuit isintroduced into the second container 110.

Then, it is checked in step S1330 whether the third container 112 stillcontains integrated circuits not yet tested.

If the third container 112 still contains integrated circuits not yettested (YES in step S1330), steps S1322, S1323, S1325, S1326 and S1327are repeatedly carried out.

If the third container 112 does no longer contain integrated circuitsnot tested (NO in step S1330), the test is ended.

The above-mentioned operation may be described as a control program andstored in a recording medium such as a floppy disc or ROM equipped withthe main controller 104 b. By carrying out the control program in themain controller 104 b, the above-mentioned operation can be repeated.

[Fourth Embodiment]

FIG. 15 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with the fourth embodiment. The illustrated apparatus iscomprised of a tester 1, an under-test integrated circuit set 12, aspectrum measurement unit 3, a main controller 4 c, a first memory 7, asecond memory 5, a calculator 6, a first set 9 comprised of integratedcircuits having been judged to have no failures, and a second set 10comprised of integrated circuits judged to have failures.

In comparison with the apparatus in accordance with the thirdembodiment, illustrated in FIG. 9, the apparatus in accordance with thefourth embodiment is designed to include the main controller 4 c inplace of the main controller 4 b. The main controller 4 c has differentfunctions from those of the main controller 4 b.

FIGS. 16 and 17 are flow-charts showing an operation of the apparatus inaccordance with the fourth embodiment.

An operation of the apparatus in accordance with the fourth embodimentis identical with the operation of the apparatus in accordance with thethird embodiment except the following step.

As shown in step S420, when an integrated circuit 8 has been judged tobe in no failure in step S418, a reference is updated. Specifically, thepower source current spectrum of the integrated circuit 8 having beenjudged to be in no failure in step S418 is transmitted into and storedin the first memory 7. The first memory 7 already stores data aboutpower source current spectrum of integrated circuits used forestablishing a reference. The calculator 6 calculates again a mean valueand standard deviation of power source current spectrum of allintegrated circuits, based on both data about the spectrum alreadystored in the first memory 7 and data about the spectrum additionallystored in the first memory 7. The thus calculated mean value andstandard deviation are stored in the first memory 7 as an updatedreference, in step S420.

The steps other than step S420 are identical with the associated stepsin the third embodiment. Specifically, steps S401 to S419 and steps S421to S431 in the fourth embodiment, illustrated in FIGS. 16 and 17 areidentical with steps S301 to S319 and steps S320 to S330 in the thirdembodiment, illustrated in FIGS. 10 and 11, respectively.

Hereinbelow is explained advantages obtained by the above-mentionedfourth embodiment.

In the third embodiment, the power source current spectrum of Nintegrated circuits having been judged to be in no failure was used toestablish a reference. Though it is preferable that a reference isestablished based on the power source current spectrum of all ofintegrated circuits to be tested, it is quite difficult to establishsuch a reference, because observation of power source current spectrumis successively carried out, and at that time an integrated circuit hasto be judged as to whether it is in failure or not.

Hence, in accordance with the fourth embodiment, a reference issuccessively updated, based on power source current spectrum of theintegrated circuits having been judged to be in no failure. Thus, thefourth embodiment can update a reference and finally establish an idealreference.

Hereinbelow is explained an example of the fourth embodiment.

FIG. 18 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with an example of the fourth embodiment. The illustratedapparatus is comprised of a logic tester 101, a spectrum measurementunit 103, a main controller 104 c, a first memory 107, a second memory105, a calculator 106, a first container 109 containing integratedcircuits having been judged to have no failures, a second container 110containing integrated circuits judged to have failures, and a thirdcontainer 112 containing integrated circuits to be tested.

In comparison with the apparatus in accordance with the thirdembodiment, illustrated in FIG. 12, the apparatus in accordance with theexample of the fourth embodiment is designed to include the maincontroller 104 c in place of the main controller 104 b. The maincontroller 104 c has different functions from those of the maincontroller 104 b.

FIGS. 19 and 20 are flow-charts showing an operation of the apparatus inaccordance with the example of the fourth embodiment.

As shown in step S1420, when an integrated circuit 108 has been judgedto be in no failure in step S1418, a reference is updated. Specifically,the power source current spectrum of the integrated circuit 108 havingbeen judged to be in no failure in step S1418 is transmitted into andstored in the first memory 107. The first memory 107 already stores dataabout power source current spectrum of integrated circuits used forestablishing a reference. The calculator 106 calculates again a meanvalue and standard deviation of power source current spectrum of allintegrated circuits, based on both data about the spectrum alreadystored in the first memory 107 and data about the spectrum additionallystored in the first memory 107. The thus calculated mean value andstandard deviation are stored in the first memory 107 as an updatedreference, in step S1420.

The steps other than step S1420 are identical with the associated stepsin the third embodiment. Specifically, steps S1401 to S1419 and stepsS1421 to S1431 in the example of the fourth embodiment, illustrated inFIGS. 19 and 20 are identical with steps S1301 to S1319 and steps S1320to S1330 in the third embodiment, illustrated in FIGS. 13 and 14,respectively.

[Fifth Embodiment]

FIG. 21 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with the fifth embodiment. The illustrated apparatus iscomprised of a tester 1, an under-test integrated circuit set 2, aspectrum measurement unit 3, a main controller 4 d, a first memory 7, asecond memory 5, a calculator 6, and a normalizer 11.

In comparison with the apparatus in accordance with the firstembodiment, illustrated in FIG. 1, the apparatus in accordance with thefifth embodiment is designed to include the main controller 4 d in placeof the main controller 4 and additionally include the normalizer 11. Themain controller 4 d has different functions from those of the maincontroller 4. The normalizer 11 is electrically connected to thespectrum measurement unit 3, normalizes power source current spectrummeasured by the spectrum measurement unit 3, and transmits the result ofnormalization to the first memory 7.

FIG. 22 is a flow-chart showing an operation of the apparatus inaccordance with the fifth embodiment. Herein, the under-test integratedcircuit set 2 containing a plurality of the same integrated circuits tobe tested is indicated with “A”. At this stage, the integrated circuitset A is identical with the under-test integrated circuit set 2.

First, integrated circuits in the integrated circuit set A are tested bythe tester 1 as to whether they are in failure or not in accordance withconventional tests, in step S501.

The results of the test are transmitted to and stored in the firstmemory 7. At the same time, integrated circuits having been judged to bein failure by the tester 1 are removed from the integrated circuit setA, in step S502.

The spectrum measurement unit 3 applies a test signal to each one ofintegrated circuits in the integrated circuit set A, that is, each oneof the integrated circuits having been judged to be in no failure amongthe under-test integrated circuit set 2 in step S501, observes a powersource current running through each one of the integrated circuits, andanalyzes a frequency of the observed current, in step S503.

Spectrum of a power source current, obtained as a result of analysis ofthe frequency, is transmitted to the normalizer 11, and then, isnormalized by the normalizer 11, in step S504. For instance, thenormalizer 11 calculates a sum of the power source current spectrum foreach one of the frequencies of the observed spectrum, and divides thesum by the power source current spectrum for each one of thefrequencies. The thus calculated quotient is defined as normalizedspectrum.

Then, the calculator 6 calculates a mean value and standard deviationfor each one of frequencies of the power source current spectrum of theintegrated circuits in the integrated circuit set A, based on thespectrum of the integrated circuits in the integrated circuit set A,stored in the first memory 7, in step S505.

In addition, the calculator 6 calculates G/SD for each one of theintegrated circuits for each one of frequencies wherein G indicates adifference between the spectrum of each one of integrated circuits inthe integrated circuit set A and the mean value, and SD indicates thestandard deviation having been calculated in step S505. If the thuscalculated G/SD is greater than the predetermined value stored in thesecond memory 5, the calculator 6 judges that an integrated circuithaving such G/SD is in failure, in step S506.

Then, it is judged in step S507 whether there has been found anintegrated circuit in failure in the integrated circuit set A.

If there has been found an integrated circuit having failures (YES instep S507), such an integrated circuit is removed from the integratedcircuit set A, in step S508, and steps S505 to S507 are repeated.

If there has not been found an integrated circuit having failures (NO instep S507), all the integrated circuits in the integrated circuit set Aare judged to be in no failure, in step S509.

Hereinbelow is explained advantaged obtained by the above-mentionedfifth embodiment.

As mentioned earlier, power source current spectrum is obtained byanalyzing a frequency of a power source current running through anintegrated circuit when a test signal is applied to the integratedcircuit. A power source current is an analog value, and hence, is likelyto be much influenced by fluctuation in processing conditions infabrication of integrated circuits. Since fluctuation in processingconditions is unavoidable, it is also unavoidable for a power sourcecurrent or power source current spectrum to be influenced by fluctuationin processing conditions.

In the fifth embodiment, since an integrated circuit is judged as towhether it is in failure or not by detecting an abnormal power sourcecurrent caused by a failure in an integrated circuit, it is necessary todistinguish fluctuation in power source current spectrum caused by afailure in an integrated circuit from fluctuation in power sourcecurrent spectrum caused by fluctuation in processing conditions.

It is considered that fluctuation in processing conditions merely causesuniform fluctuation in power source current spectrum in each of thefrequencies of the spectrum. Thus, by normalizing the power sourcecurrent spectrum in each one of the frequencies with a sum of the powersource current spectrum in all of the frequencies, it would be possibleto avoid the power source current spectrum from being influenced byfluctuation in processing conditions, ensuring higher accuracy withwhich a failure is detected.

Hereinbelow is explained one example of the fifth embodiment.

FIG. 23 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with an example of the fifth embodiment. The illustratedapparatus is comprised of a logic tester 101, an under-test integratedcircuit set 102, a spectrum measurement unit 103, a main controller 104d, a first memory 107, a second memory 105, a calculator 106, and anormalizer 111.

In comparison with the apparatus in accordance with the firstembodiment, illustrated in FIG. 1, the apparatus in accordance with theexample of the fifth embodiment is designed to include the maincontroller 104 d in place of the main controller 4 and additionallyinclude the normalizer 111. The main controller 4 d has differentfunctions from those of the main controller 4.

The normalizer 111 is electrically connected to the spectrum measurementunit 103, normalizes power source current spectrum measured by thespectrum measurement unit 103, and transmits the result of normalizationto the first memory 107.

FIG. 24 is a flow-chart showing an operation of the apparatus inaccordance with the example of the fifth embodiment.

As shown in step S1504, power source current spectrum observed by thespectrum measurement unit 103 is normalized by the normalizer 111. Thethus normalized spectrum is transmitted to and stored in the firstmemory 107.

The normalizer 111 normalizes power source current spectrum as follows,for instance.

Herein, it is assumed that power source current spectrum in each offrequencies is indicated as p(1), p(2), p(3), - - - , p(n), wherein p(i)indicates power source current spectrum at a frequency i. It is alsoassumed that a sum of power source current spectrum in all of thefrequencies is indicated as S. That is, S is defined as follows.

S=p(1)+p(2)+p(3)+ - - - +p(n)

By dividing p(i) by S, there are obtained p(1)/S, p(2)/S, p(3)/S, - - -, p(n)/S, with which the previous spectrum are replaced. Namely, p(1)/S,p(2)/S, p(3)/S, - - - , p(n)/S are used as power source current spectrumhereinafter.

The steps other than step S1504 are identical with the associated stepsin the first embodiment. Specifically, steps S1501 to S1503 and stepsS1505 to S1509 in the example of the fifth embodiment, illustrated inFIG. 24 are identical with steps S1101 to S1103 and steps S1104 to S1108in the first embodiment, illustrated in FIG. 4, respectively.

The above-mentioned operation may be described as a control program andstored in a recording medium such as a floppy disc or ROM equipped withthe main controller 104 d. By carrying out the control program in themain controller 104 d, the above-mentioned operation can be repeated.

[Sixth Embodiment]

FIG. 25 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with the sixth embodiment. The illustrated apparatus iscomprised of a tester 1, an under-test integrated circuit set 2, aspectrum measurement unit 3, a main controller 4 e, a first memory 7, asecond memory 5, a calculator 6, and a normalizer 11.

In comparison with the apparatus in accordance with the secondembodiment, illustrated in FIG. 5, the apparatus in accordance with thesixth embodiment is designed to include the main controller 4 e in placeof the main controller 4 a and additionally include the normalizer 11.The main controller 4 e has different functions from those of the maincontroller 4 a. The normalizer 11 is electrically connected to thespectrum measurement unit 3, normalizes power source current spectrummeasured by the spectrum measurement unit 3, and transmits the result ofnormalization to the first memory 7.

FIG. 26 is a flow-chart showing an operation of the apparatus inaccordance with the sixth embodiment.

An operation to be carried out in step S604 in FIG. 26 is identical withan operation to be carried out in step S504 in FIG. 22. An operation ofthe apparatus in accordance with the sixth embodiment, to be carried outin other steps is identical with an operation of the apparatus inaccordance with the second embodiment. Specifically, an operation to becarried out in steps S601, S602, S603, S605, S606, S607 and S608 in FIG.26 is identical with an operation to be carried out in steps S201, S202,S203, S204, S205, S206 and S207 in FIG. 6.

The above-mentioned operation of the apparatus in accordance with thesixth embodiment is controlled by the main controller 4 e. Theabove-mentioned operation may be described as a control program andstored in a recording medium such as a floppy disc or ROM equipped withthe main controller 4 e. By carrying out the control program in the maincontroller 4 e, the above-mentioned operation can be repeated.

The sixth embodiment provides the same advantages as those obtained bythe fifth embodiment.

Hereinbelow is explained an example of the sixth embodiment.

FIG. 27 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with the example of the sixth embodiment. The illustratedapparatus is comprised of a logic tester 101, an under-test integratedcircuit set 102, a spectrum measurement unit 103, a main controller 104e, a first memory 107, a second memory 105, a calculator 106, and anormalizer 111.

In comparison with the apparatus in accordance with the secondembodiment, illustrated in FIG. 5, the apparatus illustrated in FIG. 27is designed to include the main controller 104 e in place of the maincontroller 4 a and additionally include the normalizer 111. The maincontroller 104 e has different functions from those of the maincontroller 4 a. The normalizer 111 is electrically connected to thespectrum measurement unit 103, normalizes power source current spectrummeasured by the spectrum measurement unit 103, and transmits the resultof normalization to the first memory 107.

FIG. 28 is a flow-chart showing an operation of the apparatus inaccordance with the example of the sixth embodiment.

An operation to be carried out in step S1604 in FIG. 28 is identicalwith an operation to be carried out in step S1504 in FIG. 24. Anoperation of the apparatus in accordance with the example of the sixthembodiment, to be carried out in other steps is identical with anoperation of the apparatus in accordance with the second embodiment.Specifically, an operation to be carried out in steps S1601, S1602,S1603, S1605, S1606, S1607 and S1608 in FIG. 28 is identical with anoperation to be carried out in steps S1201, S1202, S1203, S1204, S1205,S1206 and S1207 in FIG. 8.

The above-mentioned operation of the apparatus in accordance with theexample of the sixth embodiment is controlled by the main controller 104e. The above-mentioned operation may be described as a control programand stored in a recording medium such as a floppy disc or ROM equippedwith the main controller 104 e. By carrying out the control program inthe main controller 104 e, the above-mentioned operation can berepeated.

[Seventh Embodiment]

FIG. 29 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with the seventh embodiment. The illustrated apparatus iscomprised of a tester 1, an under-test integrated circuit set 12, aspectrum measurement unit 3, a main controller 4 f, a first memory 7, asecond memory 5, a calculator 6, a normalizer 11, a first set 9comprised of integrated circuits having been judged to have no failures,and a second set 10 comprised of integrated circuits judged to havefailures.

In comparison with the apparatus in accordance with the thirdembodiment, illustrated in FIG. 9, the apparatus in accordance with theseventh embodiment is designed to include the main controller 4 f inplace of the main controller 4 b and additionally include the normalizer11. The main controller 4 f has different functions from those of themain controller 4 b. The normalizer 11 is electrically connected to thespectrum measurement unit 3, normalizes power source current spectrummeasured by the spectrum measurement unit 3, and transmits the result ofnormalization to the first memory 7 through the main controller 4 f.

FIGS. 30 and 31 are flow-charts showing an operation of the apparatus inaccordance with the seventh embodiment.

An operation to be carried out in steps S705, S717 and S728 in FIGS. 30and 31 is identical with an operation to be carried out in step S504 inthe fifth embodiment illustrated in FIG. 22. An operation of theapparatus in accordance with the seventh embodiment, to be carried outin other steps is identical with an operation of the apparatus inaccordance with the third embodiment. Specifically, an operation to becarried out in steps S701 to S704, S706 to S716, S718 to S727 and S729to S733 in FIGS. 30 and 31 is identical with an operation to be carriedout in steps S301 to S304, S305 to S315, S316 to S325 and S326 to S330in FIGS. 10 and 11, respectively.

The above-mentioned operation of the apparatus in accordance with theseventh embodiment is controlled by the main controller 4 f. Theabove-mentioned operation may be described as a control program andstored in a recording medium such as a floppy disc or ROM equipped withthe main controller 4 f. By carrying out the control program in the maincontroller 4 f, the above-mentioned operation can be repeated.

The seventh embodiment provides the same advantages as a sum of theadvantages obtained by the third embodiment and the advantages obtainedby the fifth embodiment.

Hereinbelow is explained an example of the seventh embodiment.

FIG. 32 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with the example of the seventh embodiment. The illustratedapparatus is comprised of a logic tester 101, a spectrum measurementunit 103, a main controller 104 f, a first memory 107, a second memory105, a calculator 106, a first container 109 containing integratedcircuits having been judged to have no failures, a second container 110containing integrated circuits judged to have failures, a thirdcontainer 112 containing integrated circuits to be tested and anormalizer 111.

In comparison with the apparatus in accordance with the example of thethird embodiment, illustrated in FIG. 9, the apparatus in accordancewith the example of the seventh embodiment is designed to include themain controller 104 f in place of the main controller 104 b andadditionally include the normalizer 111. The main controller 104 f hasdifferent functions from those of the main controller 104 b. Thenormalizer 111 is electrically connected to the spectrum measurementunit 103, normalizes power source current spectrum measured by thespectrum measurement unit 103, and transmits the result of normalizationto the first memory 107 through the main controller 104 f.

FIGS. 33 and 34 are flow-charts showing an operation of the apparatus inaccordance with the example of the seventh embodiment.

An operation to be carried out in steps S1705, S1717 and S1728 in FIGS.33 and 34 is identical with an operation to be carried out in step S1504in the example of the fifth embodiment, illustrated in FIG. 24. Anoperation of the apparatus in accordance with the example of the seventhembodiment, to be carried out in other steps is identical with anoperation of the apparatus in accordance with the example of the fifthembodiment. Specifically, an operation to be carried out in steps S1701to S1704, S1706 to S1716, S1718 to S1727 and S1729 to S1733 in FIGS. 33and 34 is identical with an operation to be carried out in steps S1301to S1304, S1305 to S1315, S1316 to S1325 and S1326 to S1330 in FIGS. 13and 14, respectively.

The above-mentioned operation of the apparatus in accordance with theexample of the seventh embodiment is controlled by the main controller104 f. The above-mentioned operation may be described as a controlprogram and stored in a recording medium such as a floppy disc or ROMequipped with the main controller 104 f. By carrying out the controlprogram in the main controller 104 f, the above-mentioned operation canbe repeated.

[Eighth Embodiment]

FIG. 35 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with the eighth embodiment. The illustrated apparatus iscomprised of a tester 1, an under-test integrated circuit set 12, aspectrum measurement unit 3, a main controller 4 g, a first memory 7, asecond memory 5, a calculator 6, a first set 9 comprised of integratedcircuits having been judged to have no failures, a second set 10comprised of integrated circuits judged to have failures, and anormalizer 11.

In comparison with the apparatus in accordance with the fourthembodiment, illustrated in FIG. 15, the apparatus in accordance with theeighth embodiment is designed to include the main controller 4 g inplace of the main controller 4 c and additionally include the normalizer11. The main controller 4 g has different functions from those of themain controller 4 c. The normalizer 11 is electrically connected to thespectrum measurement unit 3, normalizes power source current spectrummeasured by the spectrum measurement unit 3, and transmits the result ofnormalization to the first memory 7 through the main controller 4 g.

FIGS. 36 and 37 are flow-charts showing an operation of the apparatus inaccordance with the example of the eighth embodiment.

An operation to be carried out in steps S805, S817 and S828 in FIGS. 36and 37 is identical with an operation to be carried out in step S504 inthe fifth embodiment, illustrated in FIG. 22. An operation of theapparatus in accordance with the eighth embodiment, to be carried out inother steps is identical with an operation of the apparatus inaccordance with the example of the fourth embodiment. Specifically, anoperation to be carried out in steps S801 to S804, S806 to S816, S818 toS828 and S830 to S834 in FIGS. 36 and 37 is identical with an operationto be carried out in steps S401 to S404, S405 to S415, S416 to S426 andS427 to S431 in FIGS. 16 and 17, respectively.

The above-mentioned operation of the apparatus in accordance with theeighth embodiment is controlled by the main controller 4 g. Theabove-mentioned operation may be described as a control program andstored in a recording medium such as a floppy disc or ROM equipped withthe main controller 4 g. By carrying out the control program in the maincontroller 4 g, the above-mentioned operation can be repeated.

The eighth embodiment provides the same advantages as a sum of theadvantages obtained by the fourth embodiment and the advantages obtainedby the fifth embodiment.

Hereinbelow is explained an example of the eighth embodiment.

FIG. 38 is a block diagram of an apparatus for detecting an integratedcircuit having failures among a plurality of integrated circuits, inaccordance with the example of the eighth embodiment. The illustratedapparatus is comprised of a logic tester 101, a spectrum measurementunit 103, a main controller 104 g, a first memory 107, a second memory105, a calculator 106, a first container 109 containing integratedcircuits having been judged to have no failures, a second container 110containing integrated circuits judged to have failures, a thirdcontainer 112 containing integrated circuits to be tested and anormalizer 111.

In comparison with the apparatus in accordance with the example of thefourth embodiment, illustrated in FIG. 18, the apparatus in accordancewith the example of the eighth embodiment is designed to include themain controller 104 g in place of the main controller 104 c andadditionally include the normalizer 111. The main controller 104 g hasdifferent functions from those of the main controller 104 c. Thenormalizer 111 is electrically connected to the spectrum measurementunit 103, normalizes power source current spectrum measured by thespectrum measurement unit 103, and transmits the result of normalizationto the first memory 107 through the main controller 104 g.

FIGS. 39 and 40 are flow-charts showing an operation of the apparatus inaccordance with the example of the eighth embodiment.

An operation to be carried out in steps S1805, S1817 and S1829 in FIGS.39 and 40 is identical with an operation to be carried out in step S1504in the example of the fifth embodiment, illustrated in FIG. 24. Anoperation of the apparatus in accordance with the example of the eighthembodiment, to be carried out in other steps is identical with anoperation of the apparatus in accordance with the example of the fourthembodiment. Specifically, an operation to be carried out in steps S1801to S1804, S1806 to S1816, S1818 to S1828 and S1830 to S1834 in FIGS. 39and 40 is identical with an operation to be carried out in steps S1401to S1404, S1405 to S1415, S1416 to S1426 and S1427 to S1431 in FIGS. 19and 20, respectively.

The above-mentioned operation of the apparatus in accordance with theexample of the eighth embodiment is controlled by the main controller104 g. The above-mentioned operation may be described as a controlprogram and stored in a recording medium such as a floppy disc or ROMequipped with the main controller 104 g. By carrying out the controlprogram in the main controller 104 g, the above-mentioned operation canbe repeated.

Hereinbelow is explained an embodiment of a recording medium storing aprogram therein for accomplishing the above-mentioned apparatus andmethod.

A recording medium storing a program for accomplishing theabove-mentioned apparatus for detecting an integrated circuit havingfailures among a plurality of integrated circuits may be accomplished byprogramming functions of the above-mentioned apparatuses and systemswith a programming language readable by a computer, and recording theprogram in a recording medium such as CD-ROM, a floppy disc, a magnetictape, and any other suitable means for storing a program therein.

A hard disc equipped in a server may be employed as a recording medium.It is also possible to accomplish the recording medium in accordancewith the present invention by storing the above-mentioned computerprogram in such a recording medium as mentioned above, and reading thecomputer program by other computers through a network.

While the present invention has been described in connection withcertain preferred embodiments, it is to be understood that the subjectmatter encompassed by way of the present invention is not to be limitedto those specific embodiments. On the contrary, it is intended for thesubject matter of the invention to include all alternatives,modifications and equivalents as can be included within the spirit andscope of the following claims.

The entire disclosure of Japanese Patent Application No. 11-182726 filedon Jun. 29, 1999 including specification, claims, drawings and summaryis incorporated herein by reference in its entirety.

What is claimed is:
 1. A method of detecting an integrated circuit infailure among integrated circuits, based on spectrum which is a resultof analyzing a frequency of a current running through an integratedcircuit when a test signal is applied to said integrated circuit,without preparing data of an integrated circuit in no failure, as areference, said method comprising the steps of: (a) assuming that allintegrated circuits under test define a under-test integrated circuitset, and testing each one of said integrated circuits in said under-testintegrated circuit set to judge if any one of said integrated circuitsis in failure; (b) modifying said under-test integrated circuit set byremoving integrated circuits having been judged to be in failure in saidstep (a), from said under-test integrated circuit set; (c) measuringspectrum of a current supplied from a power source into each one of saidintegrated circuits in said under-test integrated circuit set modifiedin step (b); (d) calculating a mean value and standard deviation of saidspectrum for said under-test integrated circuit set modified in step(b); (e) judging whether said standard deviation is equal to or smallerthan a predetermined value; (f) modifying said under-test integratedcircuit set by removing an integrated circuit having specific spectrumdetermined based on said mean value, from said under-test integratedcircuit set, if said standard deviation is greater than saidpredetermined value, and repeating said steps (d), (e) and (f); and (g)judging said under-test integrated circuit set modified in said step (b)to be in no failure, if said standard deviation has been judged to beequal to or smaller than said predetermined value in said step (e). 2.The method as set forth in claim 1, further comprising the step (h) ofnormalizing said spectrum, said step (h) being carried out subsequentlyto said step (c).
 3. The method as Set forth in claim 2, wherein saidstep (h) further comprises the steps of: (h1) summing up spectrum forall frequencies to have a total; and (h2) calculating a ratio ofspectrum for each one of frequencies to said total.
 4. The method as setforth in claim 2, wherein said step (f) further includes comprises thesteps of: (f1) calculating a gap between said spectrum and said meanvalue for each one of frequencies; (f2) identifying an integratedcircuit having a maximum gap among gaps calculated in said step (f1);and (f3) removing said integrated circuit identified in said step (f2),from said under-test integrated circuit set.
 5. An apparatus fordetecting an integrated circuit in failure among integrated circuits,based on spectrum which is a result of analyzing a frequency of acurrent running through an integrated circuit when a test signal isapplied to said integrated circuit, without preparing data of anintegrated circuit in no failure, as a reference, said apparatuscomprising: (a) a tester which tests an integrated circuit as to whethersaid integrated circuit is in failure or not; (b) a spectrum measurementunit which measures spectrum of said integrated circuit; (c) a firstmemory storing said spectrum therein; and (d) a controller whichestablishes a reference, based on spectrum of the predetermined numberof integrated circuits under test, and judges whether an integratedcircuit among said integrated circuits is in failure or not, bycomparing spectrum of each one of said integrated circuits under test tosaid reference.
 6. The apparatus as set forth in claim 5, wherein saidcontroller updates said reference, based on spectrum of an integratedcircuit having been judged to be in no failure.
 7. The apparatus as setforth in claim 5, further comprising a normalizer which normalizes saidspectrum and replaces the previous spectrum with the normalizedspectrum.
 8. The apparatus as set forth in claim 6, further comprising anormalizer which normalizes said spectrum and replaces the previousspectrum with the normalized spectrum.
 9. A recording medium readable bya computer, storing a program therein for causing a computer to carryout a method of detecting an integrated circuit in failure amongintegrated circuits, based on spectrum which is a result of analyzing afrequency of a current running through an integrated circuit when a testsignal is applied to said integrated circuit, without preparing data ofan integrated circuit in no failure, as a reference, said methodcomprising the steps of: (a) assuming that all integrated circuits undertest define a under-test integrated circuit set, and testing each one ofsaid integrated circuits in said under-test integrated circuit set tojudge if any one of said integrated circuits is in failure; (b)modifying said under-test integrated circuit set by removing integratedcircuits having been judged to be in failure in said step (a), from saidunder-test integrated circuit set; (c) measuring spectrum of a currentsupplied from a power source into each one of said integrated circuitsin said under-test integrated circuit set modified in step (b); (d)calculating a mean value and standard deviation of said spectrum forsaid under-test integrated circuit set modified in step (b); (e) judgingwhether said standard deviation is equal to or smaller than apredetermined value; (f) modifying said under-test integrated circuitset by removing an integrated circuit having specific spectrumdetermined based on said mean value, from said under-test integratedcircuit set, if said standard deviation is greater than saidpredetermined value, and repeating said steps (d), (e) and (f); and (g)judging said under-test integrated circuit set modified in said step (b)to be in no failure, if said standard deviation has been judged to beequal to or smaller than said predetermined value in said step (e). 10.The recording medium as set forth in claim 9, wherein said methodfurther comprises the step (h) of normalizing said spectrum, said step(h) being carried out subsequently to said step (c).
 11. The recordingmedium as set forth in claim 10, wherein said step (h) further comprisesthe steps of: (h1) summing up spectrum for all frequencies to have atotal; and (h2) calculating a ratio of spectrum for each one offrequencies to said total.
 12. The recording medium as set forth inclaim 10, wherein said step (f) further comprises the steps of: (f1)calculating a gap between said spectrum and said mean value for each oneof frequencies; (f2) identifying an integrated circuit having a maximumgap among gaps calculated in said step (f1); and (f3) removing saidintegrated circuit identified in said step (f2), from said under-testintegrated circuit set.
 13. A recording medium readable by a computer,storing a program therein for causing a computer to act as an apparatusfor detecting an integrated circuit in failure among integratedcircuits, based on spectrum which is a result of analyzing a frequencyof a current running through an integrated circuit when a test signal isapplied to said integrated circuit, without preparing data of anintegrated circuit in no failure, as a reference, said apparatuscomprising: (a) a tester which tests an integrated circuit as to whethersaid integrated circuit is in failure or not; (b) a spectrum measurementunit which measures spectrum of said integrated circuit; (c) a firstmemory storing said spectrum therein; and (d) a controller whichestablishes a reference, based on spectrum of the predetermined numberof integrated circuits under test, and judges whether an integratedcircuit among said integrated circuits is in failure or not, bycomparing spectrum of each one of said integrated circuits under test tosaid reference.
 14. The recording medium as set forth in claim 13,wherein said controller updates said reference, based on spectrum of anintegrated circuit having been judged to be in no failure.
 15. Therecording medium as set forth in claim 13, wherein said apparatusfurther comprises a normalizer which normalizes said spectrum andreplaces the previous spectrum with the normalized spectrum.
 16. Therecording medium as set forth in claim 14, wherein said apparatusfurther comprises a normalizer which normalizes said spectrum andreplaces the previous spectrum with the normalized spectrum.